Angiotensin II is a prothrombotic vasoconstrictor. This study proves that many hypertensives are hypercoagulable and at risk for myocardial infarction. The modified recalcification time (MRT) test, used to assess hypercoagulability, incorporates the role of tissue factor in coagulation by activating the monocyte with endotoxin to release latent tissue factor. Aliquots of citrated blood obtained from hypertensives and normotensive controls were placed in two groups of vials, one with saline (group S) and one with endotoxin (group E). All vials were incubated at 37 degrees C for 2 hours, citrate neutralized with calcium chloride, and the MRT (in minutes) for group S (MRT S) and for group E (MRT E) was determined. Mean MRT S values +/- standard deviation (SD) for hypertensives (n = 25) and for controls (n = 27) were 6.4 +/- 1.2 and 6.8 +/- 1.2, respectively. The MRT E values were 4.3 +/- 1.2 and 5.7 +/- 0.9 for the hypertensives and controls, respectively. The MRT E, not the MRT S, was significant. Hypertensives had MRT E values < 4.5 minutes, and by our established criteria, were hypercoagulable. We conclude that because hypercoagulability is a risk factor for thrombosis, hypertensives with short MRT E values may be at increased risk for myocardial or other thrombotic events.